Precise, no-contact, position sensing using imaging

ABSTRACT

A contact free optical motion sensor for an inertial reference system. One or more image acquisition systems are adapted to produce a series of overlapping images of a gas bearing supported spherical inertial sensor assembly. A controller coupled to receive the series of overlapping images applies a delta detection algorithm to the series of overlapping images to determine the distance, the direction of movement of the inertial sensor assembly and the resulting relative position of the gas bearing supported spherical inertial sensor assembly. The controller further calculates the rotational velocity of the inertial sensor assembly based on a time sequence between the received series of image signals and the distance moved.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/004,743, filed on Dec. 3, 2004 and entitled “PRECISE, NO-CONTACT,POSITION SENSING USING IMAGING” (the '743 application). The '743application is incorporated herein by reference.

This application is related to and claims the benefit of the filing dateof U.S. Provisional Application No. 60/608,819 filed on Sep. 10, 2004,entitled GENERALIZED INERTIAL MEASUREMENT ERROR REDUCTION THROUGHMULTIPLE AXIS ROTATION DURING FLIGHT, which is incorporated herein byreference.

This application is related to co-pending U.S. patent application Ser.No. 11/004,184, filed on Dec. 3, 2004 and entitled “GAS SUPPORTEDINERTIAL SENSOR SYSTEM AND METHOD” (the '184 application). The '184application is incorporated herein by reference.

This application is also related to the following applications filed onDec. 3, 2004, all of which are hereby incorporated herein by reference:

U.S. patent application Ser. No. 11/004,531, entitled “SPHERICALPOSITION MONITORING SYSTEM,” Attorney Docket No. H0007169-5804 (the '531application);

U.S. patent application Ser. No. 11/004,759, entitled “ABSOLUTE POSITIONDETERMINATION OF AN OBJECT USING PATTERN RECOGNITION,” Attorney DocketNo. H0007167-1628 (the '759 application);

U.S. patent application Ser. No. 11/004,529, entitled “THREE DIMENSIONALBALANCE ASSEMBLY,” Attorney Docket No. H0007914-1628 (the '529application);

U.S. patent application Ser. No. 11/004,452, entitled “ARTICULATED GASBEARING SUPPORT PADS,” Attorney Docket No. H0006475-1628 (the '452application);

U.S. patent application Ser. No. 11/004,214, entitled “GAS JET CONTROLFOR INERTIAL MEASUREMENT UNIT,” Attorney Docket No. H0006535-1628 (the'214 application);

U.S. patent application Ser. No. 11/004,177, entitled “RF WIRELESSCOMMUNICATION FOR DEEPLY EMBEDDED AEROSPACE SYSTEMS,” Attorney DocketNo. H0006345-1629 (the '177 application); and

U.S. patent application Ser. No. 11/004,517, entitled “GENERALIZEDINERTIAL MEASUREMENT ERROR REDUCTION THROUGH MULTIPLE AXIS ROTATIONDURING FLIGHT,” Attorney Docket No. H0006368-1628 (the '517application).

TECHNICAL FIELD

The present invention generally relates to the field of motion sensorsand in particular to contact free optical motion sensing for inertialreference systems.

BACKGROUND

Precision inertial navigation systems typically require concentric setsof ball bearing supported gimbals which allow instruments to freelyrotate in flight maneuvers and allow them to be manipulated forcalibration. The embodiments of the previously referenced '6540application, which is herein incorporated by reference, eliminate theneed for gimbals and ball bearings by supporting the inertial sensorassembly with a spherically shaped gas bearing. The gas bearing allowsrotation of the inertial sensor assembly in all axes with no wear due tocontact between rotating surfaces. However, because physical contactwith the freely rotating inertial sensor assembly is undesirable, theneed arises to sense the motion of the inertial sensor assembly withoutphysical contact between the sensor and the assembly.

An optical computer mouse is one example of a low cost sensor thatdetects relative movement with respect to a flat surface without theneed for physical contact between the mouse and the surface. The opticalmouse system includes an image acquisition system (IAS) and a digitalsignal processor (DSP). The IAS forms an image of the microscopictextural features of the surface below the sensor. A sequence of theseimages is taken quickly so that the sequential pictures overlap. Theimages are processed by the DSP to determine the relative direction anddistance of motion between the surface and the sensor. The DSP furtherproduces a stream of relative delta-x and delta-y displacement valuesalong the x and y axis. The resulting displacement data is provided bythe output of the mouse to the computer. The data is used by thecomputer to relocate an on-screen pointer in coordination with movementof the mouse.

The algorithms translating mouse movement into cursor movement arenonlinear in order to aid the user with quickly selecting the desiredobject on the monitor. A human viewing the computer screen and operatingthe mouse provides the required feedback loop to ensure that cursorcontrolled by the mouse is accurately positioned on the screen. Precisecalculations of the exact distance, direction and velocity of relativemotion between the mouse sensor and surface are not necessary for thisapplication and thus are not determined. For these reasons, the opticalnavigation system applied by optical computer mice is inadequate inapplications where the precise direction and distance of displacementand velocity of an object is required.

For the reasons stated above and for other reasons stated below whichwill become apparent to those skilled in the art upon reading andunderstanding the specification, there is a need in the art for contactfree precision motion detection system.

SUMMARY

The Embodiments of the present invention address the problem of sensingand measuring the movement of an object, where physical contact with theobject is undesirable, through the use of optical imaging.

In one embodiment, a motion detection system is disclosed. One or moreoptical sensors each generate image signals of an object. A controlleris coupled with each sensor to receive the image signals and adapted toapply a delta detection algorithm to the image signals to determine thedistance and direction the object has moved. The controller furthercalculates the velocity of the object's movement based on a timesequence between the received series of image signals and the distancemoved.

In another embodiment, another motion detection system is disclosed. Oneor more image acquisition systems are adapted to produce a series ofoverlapping images of the object. A controller is coupled to receive theseries of overlapping images from each image acquisition system. Thecontroller measures the elapsed time between images in the series, andapplies a delta detection algorithm to the series of overlapping imagesin order to determine the distance and direction the object has moved.The controller calculates the velocity of the object's movement based onthe elapsed time between images and the distance moved.

In another embodiment, a rotational displacement sensing apparatus foran inertial navigation system containing a gas bearing supportedspherical inertial sensor assembly is disclosed. One or more imageacquisition systems are adapted to produce a series of overlappingimages of the inertial sensor assembly. A controller coupled to receivethe series of overlapping images applies a delta detection algorithm tothe series of overlapping images to determine the distance, thedirection of movement of the inertial sensor assembly and the resultingrelative position of the gas bearing supported spherical inertial sensorassembly. The controller further calculates the rotational velocity ofthe inertial sensor assembly based on a time sequence between thereceived series of image signals and the distance moved.

In still another embodiment, a method for precisely determining therelative movement and velocity of a moving object is disclosed. Themethod comprising capturing a first image of the object precisely at afirst known time; capturing a second image of the object precisely atsecond known time such that the first and second images are taken insufficiently proximate times that the first and second images areoverlapping images of the object; and processing the first and secondimages through a delta detection algorithm, where the delta detectionalgorithm determines how far the object has moved, the direction ofmovement, and the rate of change in position of the object.

In still another embodiment, another method for precisely determiningthe relative movement and velocity of a moving object is disclosed. Themethod comprising capturing a first image of the object; associating atime stamp reference to the first image; capturing a second image of theobject, where the first and second images are taken in sufficientlyproximate times so that the first and second images are overlappingimages of the object; associating a time stamp reference to the secondimage; determining the direction of movement and distance moved by theobject by applying a delta detection algorithm to the images; anddetermining the velocity of the object based on the distance moved andthe difference in time between the time stamp references associated withthe images.

In yet another embodiment, another method for precisely determining therelative movement and velocity of a moving object is disclosed. Themethod comprising capturing a plurality of images of the object; whereeach image is taken in sufficiently proximate time so that subsequentimages are overlapping images of the object; associating a time stampreference to each of the images captured; determining the direction ofmovement and distance moved by the object by applying a delta detectionalgorithm to the images; and determining the velocity of the objectbased on the distance moved and the difference in time between the timestamp references associated with the images.

In yet another embodiment, another method for precisely determining therelative movement and velocity of a moving object is disclosed. Themethod comprising aligning an optical computer mouse sensor to thesurface of an object; coupling the optical mouse sensor to a computerI/O port; accumulating x-axis and y-axis displacement data communicatedby the optical computer mouse sensor to the computer I/O port, from timeT1 to time T2; calculating the distance and direction of movement of theobject, the average velocity of movement, and the resulting relativeposition of the object.

In still another embodiment, another motion detection system isdisclosed. One or more optical computer mice are aligned to captureimages of an object. A computer is coupled to receive x-axis and y-axisdisplacement data generated by the mice and to accumulate the x-axis andy-axis displacement over a time interval. The computer is furtheradapted to calculate the distance and direction of movement of theobject, the average velocity of movement, and the resulting relativeposition of the object.

In yet another embodiment, a method for precisely determining therelative movement and velocity of a moving object, where the method isembedded in a computer-readable medium is disclosed. The methodcomprising capturing a first image of an object precisely at a firstknown time; capturing a second image of the object precisely at secondknown time, where the first and second images are taken in sufficientlyproximate times so that the first and second images are overlappingimages of the object; processing the first and second images through adelta detection algorithm, where the delta detection algorithmdetermines how far the object has moved, the direction of movement; andcalculating the velocity of the object.

DRAWINGS

The present invention can be more easily understood and furtheradvantages and uses thereof more readily apparent, when considered inview of the description of the preferred embodiments and the followingfigures in which:

FIGS. 1 a and 1 b are diagrams illustrating precise, no-contact,position sensing using imaging, with an object having a planar surface.FIG. 1 a is a side view of the current invention and FIG. 1 b is a frontview of the current invention;

FIG. 2 is a diagram illustrating precise, no-contact, position sensingusing imaging, with an object having a spherical surface, of the currentinvention;

FIG. 3 is a flow chart illustrating the processing of data in oneembodiment of the current invention;

FIG. 4 is a diagram illustrating the combination of precise, no-contact,position sensing using imaging, in combination with a gas supportedinertial sensor assembly; and

FIG. 5 is a flow chart of one embodiment of the present invention.

In accordance with common practice, the various described features arenot drawn to scale but are drawn to emphasize features relevant to thepresent invention. Reference characters denote like elements throughoutFigures and text.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings that form a part hereof, and in which is shown byway of illustration specific illustrative embodiments in which theinvention may be practiced. These embodiments are described insufficient detail to enable those skilled in the art to practice theinvention, and it is to be understood that other embodiments may beutilized and that logical, mechanical and electrical changes may be madewithout departing from the spirit and scope of the present invention.The following detailed description is, therefore, not to be taken in alimiting sense.

Precision inertial navigation systems typically require concentric setsof ball bearing supported gimbals which allow instruments to freelyrotate in flight maneuvers and allow them to be manipulated forcalibration. The embodiments of the previously referenced commonlyassigned '6540 application, which is herein incorporated by reference,eliminate the need for gimbals and ball bearings by supporting theinertial sensor assembly with a spherically shaped gas bearing. The gasbearing allows rotation of the inertial sensor assembly in all axes withno wear due to contact between rotating surfaces. However, because thegas bearing eliminates physical reference points provided by thegimbals, and because physical contact with the freely rotating inertialsensor assembly is undesirable, the need arises to sense the motion,velocity and position of the inertial sensor assembly, without physicalcontact between the sensor and the assembly. The embodiments of thepresent invention address the problems of contact free motion sensing byapplying optical navigation technology to create precision, no-contactmotion sensing.

In FIGS. 1 a and 1 b, a motion detection system 100 of one embodiment ofthe present invention is illustrated. FIG. 1 a is a side view of themotion detection system 100 adapted to determine the precise relativemotion of the surface of an object 110 with respect to the opticalsensor 102. FIG. 1 b is a front view of the same embodiment. An opticalsensor 102, also commonly referred to as an image acquisition system, isrigidly connected by a mounting bracket 104 to a fixed referencestructure 106. The output of the optical sensor 102 is connected 109with a controller 108. The optical sensor 102 captures a sequence ofoverlapping images of the subject object 110 and communicates theseimages to the controller 108. The controller applies a delta detectionalgorithm to the sequence of images which determines how common featuresin the images moved from one image to the next, along the x-axis andy-axis. The delta detection algorithm then determines the distance anddirection that the object 110 has moved and calculates its new position112 relative to its previous position 111. Additionally, the controllercreates a time stamp for each image by incorporating data on therelative time each image was captured. By associating a time stamp witheach image the time elapsed between images is known. The velocity of theobject's movement is then calculated by the controller. The resultingvelocity, direction, and displacement output is then available to othersystems for such applications as process controls or process monitoring,or as error correction feedback data.

In FIG. 2, a motion detection system 200 of another embodiment of thepresent invention is illustrated. In this embodiment, the subject objectis a sphere 202 that is free to rotate 204 about an axis 206. An opticalsensor 202, also commonly referred to as an image acquisition system, isrigidly connected by a mounting bracket 204 to a fixed referencestructure 206. The output of the optical sensor 202 is connected 209with a controller 208. The optical sensor 202 captures a sequence ofoverlapping images of the subject object 210 and communicates theseimages to the controller 208. In this embodiment, the x-axis and y-axisdisplacement data provided by delta detection algorithm is used by thecontroller 208 to determine the sphere's angle of rotation, its speed ofrotation, and the resulting sphere position relative to the previousposition. Although FIG. 2 only illustrates the subject object rotatingabout a single axis, this motion detection system can be applied to aspherical object rotating on multiple axes. Embodiments of the presentinvention can be used for applications such as measuring the position ormovement of raw material in a manufacturing process, for sensing theposition of gyroscopes with respect to a fixed housing, robot motionsensing for feedback control, sensing product position in assembly andproduction facilities, or other systems requiring precision,contact-free, position sensing.

In FIG. 3, a motion detection system 300 of another embodiment of thepresent invention is illustrated, precisely detecting the motion andvelocity of an object using an off the shelf computer optical mousesensor 301 coupled 303 to an Intel based personal computer (PC) runningthe Microsoft Windows operating system 302. Internal to the opticalmouse sensor 301, the optical navigation technology creates a sequenceof images 301-1 of the surface of an object in front of the sensor. Adigital signal processor 301-2 generates a stream of x-axis and y-axisdisplacement values proportional to the relative movement of the surfaceof the object with respect to the sensor. These displacement values areformatted by the PS/2 output converter 301-3 into the proper protocol tocommunicate the values to a standard PS/2 mouse I/O device port. At thePC 302, the data from the optical mouse sensor 301 is received at thePS/2 mouse I/O device port 302-1. This embodiment of the presentinvention includes a software program running on the PC 302 whichenables the mouse sensor 301 to be used as a precision motionmeasurement instrument instead of a pointing device. The programreceives the data from the PS/2 mouse I/O port 302-1 by applyingMicrosoft's DirectInput application programming interface (API) 302-2.Microsoft's DirectInput API is an application programming interface forinput devices that communicates directly with device hardware driversand gives faster access to input data than by relying on MicrosoftWindows messages. Because DirectInput works directly with the mousedriver, it bypasses the Microsoft Windows subsystem that normallyinterprets mouse data for windows applications. The software programaccumulates the linear x-axis and y-axis displacement values 302-3 itreceives from the PS/2 mouse I/O device port 302-1 and then calculatesthe distance and direction of movement, the average velocity ofmovement, and the resulting new relative position of the object 302-4.

In other embodiments, the optical mouse sensor 301 and the PC 302 cancommunicate via a standard universal serial bus, wirelessly, or throughother communication standards, rather than through the PS/2 mouse port.In other embodiments, the optical mouse sensor 301 can be an assemblyconstructed from individual component parts rather than an off-the-shelfoptical computer mouse. Moreover, instead of a PC 302 the computersystem processing the data can be comprised of any computer systemconfigured to communicate with the optical mouse sensor 301. Because thesurface of the object observed by the optical mouse sensor 301 may beeither linearly flat in the x-y plane, or may be a nonlinear surfacesuch as a sphere, in other embodiments, the mathematical algorithms302-3 can be adjusted to map the x-axis and y-axis displacement datainto spherical coordinates, cylindrical coordinates, or other system ofcoordinates in order to calculate the objects direction and distance ofmovement and the new relative position of the object.

In FIG. 4, a motion detection system 401, in combination with the GasSupported Inertial Sensor Assembly 400 of the '6540 application of thepreferred embodiment of the present invention is illustrated. A gassupported inertial navigation system (INS) 400 utilizes a freelyrotating spherically shaped inertial sensor assembly (ISA) 408. The ISAis supported, or floats, within a spherically shaped gas bearing 402generated by a plurality of gas pads 404-1, 404-2 (only two of which areshown in FIG. 4). Pressurized gas is applied to the gas pads 404-1,404-2 and the ISA 408 rides supported on a cushion of gas with little orno contacts between the ISA and the gas pads. In one embodiment, the gasis air. The frictionless gas bearing 402 allows the ISA 408 to rotate onall axes 416. In this embodiment, optical sensors 406 and 414 aresecured to the outer shell assembly 410 of the INS 400 by brackets 413and 415. Additional details regarding the gas bearing 402, gas pads 404and the INS 400 are found in the '6540 application herein incorporatedby reference. Overlapping images of the inertial sensor assembly 408 arecaptured by the optical sensors 406, 414 and communicated 411,417 to acontroller 412 where the images are processed through a delta detectionalgorithm to determine delta-x and delta-y displacement of the images,and the relative change in position between the outer shell assembly 410and the ISA 408. The controller also calculates the velocity of rotationof the inertial sensor assembly 408 based on the precise time each imagewas captured. In order to improve accuracy when sensing movement of theISA 408 along two or more axis, the controller in this embodimentanalyses images from two optical sensors 406, 414. Incorporating datafrom two or more optical sensors allows implementation of better errorcorrection algorithms.

In FIG. 5, a method for precisely determining the relative motion of amoving object 500 of an embodiment of the present invention isillustrated. The method comprising: capturing a first image of theobject at time T1 (501); capturing a second image of the objectprecisely at time T2 (502), where the first and second images are takenin sufficiently proximate times so that the first and second images areoverlapping images of the object. Processing the first and second imagesthrough a delta detection algorithm (503), where the delta detectionalgorithm determines how far the object surface has moved along thex-axis and y-axis. Calculating the direction and distance of movement,the rate of change in position of the object, and the resulting positionof the object (504). Outputting the resulting position and velocity ofthe object (505).

Several means are available to implement the controller element of thecurrent invention. These means include, but are not limited to, digitalcomputer systems, programmable controllers, or field programmable gatearrays. Therefore other embodiments of the present invention are programinstructions resident on computer readable media which when implementedby such controllers, enable the controllers to implement embodiments ofthe present invention. Computer readable media include any form ofcomputer memory, including but not limited to magnetic disk or tape,CD-ROMs, DVD-ROMs, or any optical data storage system, flash ROM,non-volatile ROM, or RAM.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement, which is calculated to achieve the same purpose,may be substituted for the specific embodiment shown. This applicationis intended to cover any adaptations or variations of the presentinvention. Therefore, it is manifestly intended that this invention belimited only by the claims and the equivalents thereof.

1. A motion detection system comprising: one or more optical sensors,each optical sensor adapted to generate image signals of an object; anda controller coupled to receive the image signals from each opticalsensor, the controller adapted to apply a delta detection algorithm to aseries of the image signals to determine the distance and direction theobject has moved, the controller further adapted to calculate thevelocity of the object's movement based on a time sequence between thereceived series of image signals and the distance moved.
 2. The motiondetection system of claim 1, wherein the controller is further adaptedto calculate the resulting position of the object relative to theoriginal position of the object.
 3. The motion detection system of claim1, further comprising: one or more housings, each optical sensor locatedin an associated housing.
 4. The motion detection system of claim 3,further comprising: a solid mounting surface, each housing attached tothe solid mounting surface.
 5. The motion detection system of claim 4,wherein the controller is located in one of the housings.
 6. The motiondetection system of claim 5, where the object is an inertial sensorassembly for an inertial navigation system.
 7. A motion detection systemcomprising: one or more image acquisition systems, each imageacquisition system adapted to produce a series of overlapping images ofthe object; and a controller coupled to receive the series ofoverlapping images from each image acquisition system, the controlleradapted to measure the elapsed time between images received in theseries, the controller further adapted to apply a delta detectionalgorithm to the series of overlapping images to determine the distanceand direction the object has moved, and further adapted to calculate thevelocity of the object's movement based on the elapsed time betweenimages and the distance moved.
 8. The motion detection system of claim7, wherein the controller is further adapted to calculate the resultingposition of the object relative to the original position of the object.9. The motion detection system of claim 7, further comprising: one ormore housings, each optical sensor located in an associated housing. 10.The motion detection system of claim 9, further comprising: a solidmounting surface, each housing attached to the solid mounting surface.11. The motion detection system of claim 10, wherein the controller islocated in one of the housings.
 12. The motion detection system of claim11, wherein the object is an inertial sensor assembly for an inertialnavigation system.
 13. A motion detection system comprising: one or moreoptical computer mouses, each optical computer mouse adapted to generateimage signals of an object; a computer coupled to receive x-axis andy-axis displacement data communicated by the one or more opticalcomputer mouses, the computer adapted to accumulate the x-axis andy-axis displacement data from the one or more optical computer mousesover a time interval, the computer further adapted to calculate at leastone of the distance and direction of movement of the object, the averagevelocity of movement, and the resulting relative position of the object.14. The method of claim 13, wherein the computer is coupled to one ormore of the optical computer mouses through input/output ports.
 15. Themethod of claim 13, wherein the computer is coupled to one or more ofthe optical computer mouses through universal serial bus ports.
 16. Themethod of claim 13, wherein the computer is coupled to one or more ofthe optical computer mouses through standard PS2/Mouse ports.
 17. Themethod of claim 13, wherein the computer is coupled to one or more ofthe optical computer mouses through wireless ports.